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NOTE When the drawing lighting units are photometric, the attenuation type
property becomes disabled. Photometric lights have fixed, inverse-square
attenuation. The hotspot falloff attenuation in the rendered image varies from
standard lighting, as it uses a different mathematical basis.
Use Weblights
Weblights are photometric lights with customized, real-world light
distributions.
Overview of Weblights
Weblights are photometric lights with customized, real-world light
distributions.
A weblight (web) is a 3D representation of the light intensity distribution of
a light source. Weblights can be used to represent anisotropic (non-uniform)
light distributions derived from data provided by manufacturers of real-world
lights. This gives a far more precise representation of the rendered light than
either spot or point lights are capable of.
This directional light distribution information is stored in a photometric data
file in the IES format using the IES LM-63-1991 standard file format for
photometric data. You can load photometric data files provided by various
manufacturers under the Photometric Web panel in the Properties Inspector
palette for the light. The light icon represents the photometric web you select.
A light that uses a photometric web can be added to a drawing by entering
the commands WEBLIGHT and FREEWEB at the command prompt. The
WEBLIGHT command creates a targeted weblight, whereas the FREEWEB
command creates a weblight without an explicit target.
To describe the directional distribution of the light emitted by a source,
AutoCAD approximates the source by a point light placed at its photometric
center. With this approximation, the distribution is characterized as a function
of the outgoing direction only. The luminous intensity of the source for a
predetermined set of horizontal and vertical angles is provided, and the system
can compute the luminous intensity along an arbitrary direction by
interpolation.
NOTE Web distribution is used only in rendered images. Weblights are
approximated as point lights in the viewport.
Add Lighting to Your Model | 721
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